The present invention relates to a valve driving device for an engine, and more specifically to a valve driving device equipped with a variable valve timing mechanism capable of changing a rotational phase of a camshaft with respect to a crankshaft of an engine.
Recently, engines for vehicles have been equipped with a valve driving device for changing valve timing (open and/or close timing) of an intake valve and/or an exhaust valve to increase engine power, improve gas mileage and so on. In general, the valve driving device includes a hydraulic (oil) pressure operating type of variable valve timing mechanism operative to change valve timing by changing a rotational phase of a camshaft with respect to a crankshaft of the engine. An example of such mechanism is disclosed in Japanese Patent Laid-Open Publication No. 11-280414.
In a variable valve timing mechanism disclosed in the above-described publication, a rotor is fixed to one end of an intake camshaft and a housing (casing) is fixed to a sprocket (pulley) which is attached so as to be relatively rotatable with respect to the intake camshaft. Further, the rotor and the housing jointly form a hydraulic (oil) pressure chamber for advance timing (a pressure receiving chamber at advance timing side) and a hydraulic (oil) pressure chamber for delay timing (a pressure receiving chamber at delay timing side). When a hydraulic (oil) pressure control valve for controlling a supply of operating hydraulic (oil) pressure allows the operating hydraulic pressure to act on the hydraulic pressure chamber for advance timing, the rotor is rotated slightly with respect to the housing in a rotational direction of the intake camshaft. As a result, the valve timing of the intake valve advances. On the other hand, when the hydraulic pressure control valve allows the operating hydraulic pressure to act on the hydraulic pressure chamber for delay timing, the rotor is rotated with respect to the housing in an opposite direction to the rotation of the intake camshaft. As a result, the valve timing of the intake valve delays.
Further, a sensor rotor (sensing plate) is attached to the intake camshaft and a rotational angle sensor (cam-angle sensor) is disposed close to the sensor rotor. The rotational angle sensor detects a rotational phase of the intake camshaft, i.e., valve timing of the intake valve.
Such rotational angle sensor includes a detecting end surface. In general, since the detecting end surface of the sensor is located inside of a cylinder head cover of the engine, mists of lubricant oil splashed in the cylinder head adhere on the detecting surface of the sensor. Meanwhile, particulates, such as metal particulates generated by metal parts contacting each other and sworn off, get mixed in the lubricant oil. Most particulates are trapped by an oil filter and the like and then took out of the lubricant oil. However, some particulates remain in the lubricant oil without being trapped, and those particulates may accumulate on the detecting end surface of the sensor. This may cause a problem that the detecting end surface of the rotational angle sensor is covered inappropriately with such particulates, result in deterioration of detecting accuracy of the sensor.
The present invention has been devised in view of the above-described problems, and an object of the present invention is to provide a valve driving device for an engine that maintains properly detecting accuracy of a rotational sensor disposed close to a camshaft.
In order to achieve the above-described object, the first aspect of the present invention provides a valve driving device for an engine, comprising a variable valve timing mechanism disposed at an end portion of a camshaft driving an intake valve and/or an exhaust valve synchronously with a crankshaft of the engine, the variable valve timing mechanism being a hydraulic-pressure operating type of variable valve timing mechanism that is capable of changing a rotational phase of the camshaft with respect to the crankshaft, a hydraulic pressure control valve operative to control a supply of an operating hydraulic pressure to the variable valve timing mechanism, a rotational angle sensor operative to detect a rotational angle of the camshaft, the rotational angle sensor being a solenoid-pickup type of sensor and including a detecting end surface that is disposed close to a rotational area of a sensor rotor attached to the camshaft. Herein, the hydraulic pressure control valve includes a drain hole, return oil from the variable valve timing mechanism is discharged through the drain hole of the hydraulic pressure control valve, and the rotational angle sensor and the hydraulic pressure control valve are disposed such that the detecting end surface of the rotational angle sensor is located in a spray area of the return oil discharged through the drain hole.
While the variable valve timing mechanism changes a rotational phase of the camshaft, the return oil is discharged through the drain hole of the hydraulic pressure control valve. According to the valve driving device of the first aspect of the invention, the discharged return oil can be directed toward the detecting end surface of the rotational angle sensor. Accordingly, the detecting end surface can be prevented from being covered inappropriately with the metal particulates or the like, thereby maintaining properly detecting accuracy of the rotational sensor without any other particular measures.
The second aspect of the present invention provides the valve driving device for an engine of the first aspect of the invention, wherein the hydraulic pressure control valve further includes a spool, a holder for retaining the spool and a solenoid for driving the spool, and the drain hole is formed at the holder.
According to the valve driving device of the second aspect of the invention, the first aspect of the invention is further materialized for the hydraulic pressure control valve and the drain hole. Further, for example, it may be possible to have a cam cap, which supports the camshaft from above, function as the holder. In this case, the device may have the advantage of a simple structure with small-number parts and compactness.
The third aspect of the present invention provides the valve driving device for an engine the first aspect of the invention, wherein the rotational angle sensor is attached to a portion of a cylinder head cover that is close to the hydraulic pressure control valve.
According to the valve driving device of the third aspect of the invention, since it is relatively easy to attach some parts to the cylinder head cover, this can improve flexibility of selection or adjustability of attaching place for the rotational angle sensor. Further, the close location of the rotational angle sensor with respect to the hydraulic pressure control valve can assure the washing function of the detecting end surface of the rotational angle sensor by the return oil.
The fourth aspect of the present invention provides the valve driving device for an engine of the second aspect of the invention, wherein the hydraulic pressure control valve is disposed such that an axis of the spool thereof extents substantially in a vertical direction of the engine.
In general, the drain hole of the hydraulic pressure control valve is configured so as to be flat shaped, having its long axis perpendicular to the axis of the spool. Accordingly, a spray of the return oil discharged through the drain hole spreads in a horizontal direction. Thus, according to the valve driving device of the fourth aspect of the invention, it can be relatively easy for the detecting end surface of the rotational angle sensor to be located in the return oil""s spray area spread in the horizontal direction with its close position to the sensor rotor, thereby improving flexibility of its location. Since generally it would be preferred from designing stand point to have more flexibility in the horizontal direction than that in the vertical direction for parts of the engine, the above-described disposition of the hydraulic pressure control valve is meaningful.
The fifth aspect of the present invention provides the valve driving device for an engine of the first aspect of the invention, wherein the rotational angle sensor is disposed so as to locate close to and at the front of the drain hole of the hydraulic pressure control valve with respect to a rotational direction of the camshaft.
According to the valve driving device of the fifth aspect of the invention, the return oil discharged through the drain hole of the hydraulic pressure control valve can be positively carried toward the rotational angle sensor by the rotation of the sensor rotor attached to the exhaust camshaft. As a result, the amount of oil carried to the detecting end surface increases. Thus, it can promote washing of the detecting end surface of the rotational angle sensor by the return oil.
The sixth aspect of the present invention provides valve driving device for an engine, comprising a variable valve timing mechanism disposed at an end portion of a camshaft driving an intake valve and/or an exhaust valve synchronously with a crankshaft of the engine, the variable valve timing mechanism being a hydraulic-pressure operating type of variable valve timing mechanism that is capable of changing a rotational phase of the camshaft with respect to the crankshaft, a hydraulic pressure control valve operative to control a supply of an operating hydraulic pressure to the variable valve timing mechanism, the hydraulic pressure control valve including a spool, a holder for retaining the spool and a solenoid for driving the spool, a rotational angle sensor operative to detect a rotational angle of the camshaft, the rotational angle sensor being a solenoid-pickup type of sensor and including a detecting end surface that is disposed close to a rotational area of a sensor rotor attached to the camshaft. Herein, the hydraulic pressure control valve further includes a drain hole that is formed at the holder, return oil from the variable valve timing mechanism is discharged through the drain hole of the hydraulic pressure control valve, and the rotational angle sensor and the hydraulic pressure control valve are disposed close to each other such that a spray of the return oil discharged through the drain hole is directed toward the detecting end surface of the rotational angle sensor.
According to the valve driving device of the sixth aspect of the invention, substantially the same functions and effects as the above-described first aspect of the invention can be obtained.
The seventh aspect of the present invention provides the valve driving device for an engine of the sixth aspect of the invention, wherein the rotational angle sensor is attached to a portion of a cylinder head cover that is close to the hydraulic pressure control valve.
The eighth aspect of the present invention provides the valve driving device for an engine of the sixth aspect of the invention, wherein the hydraulic pressure control valve is disposed such that an axis of the spool thereof extents substantially in a vertical direction of the engine.
The ninth aspect of the present invention provides the valve driving device for an engine of the sixth aspect of the invention, wherein the rotational angle sensor is disposed so as to locate close to and at the front of the drain hole of the hydraulic pressure control valve with respect to a rotational direction of the camshaft.
According to the valve driving device of the seventh though ninth aspects of the invention, substantially the same functions and effects as the above-described third through fifth aspects of the invention can be obtained respectively.
The tenth aspect of the present invention provides the valve driving device for an engine of the sixth aspect of the invention, wherein the holder of the hydraulic pressure control valve is formed of a cam cap that supports the camshaft rotatably together with a cylinder head of the engine.
According to the valve driving device of the tenth aspect of the invention, since the cam cap is used so as to function as the holder for retaining the spool of the hydraulic pressure control valve, this can provide the advantage of a simple structure with small-number parts and compactness.